The present invention relates to a modifier for lubricating greases and a high-lubricity grease comprising a grease containing a solid lubricant therein.
A lubricating grease is a substance which, when introduced in a driving mechanism of a machine or apparatus, lubricates a driving part of the driving mechanism to thereby improve the durability of the components of the driving mechanism. Among greases is a high-lubricity grease comprising a grease containing a solid lubricant therein, such as the solid-lubricant-containing grease proposed in Japanese Patent Laid-Open No. 12791/1986. This kind of high-lubricity grease exerts excellent lubricity on high-hardness metallic parts made of a steel material. As the solid lubricant has hitherto been employed one or more substances comprising polytetrafluoroethylene as the main component.
Lubricating greases gradually alter during use. As the alteration proceeds to an excessive degree, the lubricity is considerably reduced or is lost, making the machine or apparatus unusable. Especially when the driving part of the driving mechanism of the machine or apparatus is disposed in an atmosphere rich in water or moisture, water is apt to come into the lubricating grease present in the driving part. In case where water has come into the lubricating grease, the water in the lubricating grease functions to gradually corrode or deteriorate the components of the driving part. During this corrosion or deterioration, the components of the driving part suffer lubrication failures, etc. Consequently, not only the driving part but also the driving mechanism has a considerably shortened life. As a result, it becomes necessary to replace the components of the driving part of the driving mechanism in an early stage.
On the other hand, when components of the driving part of a driving mechanism, e.g., the gears of a geared motor, have poor compatibility with each other, the driving part makes a strange noise such as, e.g., gear creaking to give a warning on an abnormal state thereof. Although the work may be required to replace the components of the driving part upon reception of the warning on an abnormal state, there frequently are cases where the components of this driving part have suffered little corrosion or deformation. In this case, the compatibility between the components of the driving part should be improved with a lubricating grease.
Accordingly, an aim of a first aspect of the invention is to eliminate those problems by modifying a lubricating grease. In particular, the aim is to provide a modifier for lubricating greases which is capable of attaining the desired modification.
The first aspect of the invention provides a lubricating-grease modifier for addition to and modification of a lubricating grease which is to be present in a driving mechanism of a machine or apparatus and lubricate a driving part of the driving mechanism, the modifier comprising a lubricating resin powder and a water-absorbing resin powder as effective ingredients.
In the lubricating-grease modifier of the first aspect of the invention the proportion by weight of the lubricating resin powder to the water-absorbing resin powder is preferably in the range of from 1:4 to 4:1. The lubricating resin powder as a component of the composition is preferably made of at least one member selected from the group consisting of polyethylene, polypropylene, nylons, polyesters, and polytetrafluoroethylene, and the water-absorbing resin powder is preferably made of at least one member selected from the group consisting of poly(acrylic acid salt) resins, poly(ethylene oxide) resins, vinyl acetate copolymer resins, and acrylic acid graft copolymer resins. The modifier can be used in such a manner that the modifier is added to and mixed with a lubricating grease beforehand, or that the modifier, according to need, is added to and mixed with a lubricating grease present in a driving mechanism of a machine or apparatus.
When the lubricating grease to which the first aspect of the invention is to be applied is used in a machine or apparatus having a driving mechanism whose driving part is placed in an atmosphere rich in water or moisture, then water is apt to come into the lubricating grease present in the driving part. In case where water has come into the lubricating grease, the water in the lubricating grease functions to gradually corrode or deteriorate the driving part. During this corrosion or deterioration, the driving part suffers lubrication failures, etc. As a result, not only the components of the driving part but also the driving mechanism has a considerably shortened life.
However, in the case where the lubricating grease contains the modifier of the first aspect of the invention, the water which is coming into the lubricating grease is taken up by the water-absorbing resin powder as a component of the modifier and is hence prevented from diffusing into the lubricating grease. Because of this, the lubricating grease exhibits its lubricity in the same state as the water-free state to lubricates the components of the driving part of the driving mechanism.
Consequently, by using the lubricating grease containing the modifier of the first aspect of the invention, the water which has come into the grease is prevented from corroding the components of the driving part. Since the components of the driving part are prevented from corroding and the driving part is hence prevented from suffering lubrication failures attributable to corrosion and from thus deteriorating, not only the life of the components of the driving part but also that of the driving mechanism can be greatly improved. As a result, the necessity of replacing the components of the driving part of the driving mechanism in an early state is eliminated.
On the other hand, in the case where components, e.g., gears, of the driving part of a driving mechanism have poor compatibility with each other, the driving part makes a strange noise such as, e.g., gear creaking to give a warning on an abnormal state thereof even when the components of the driving part are almost free from corrosion, deterioration, and deformation.
In that case, it is effective to use a grease containing the modifier incorporated therein beforehand as the lubricating grease to be applied to that driving part or to add the modifier composition, upon the noise production, to the lubricating grease present in the driving part. Particles of the lubricating resin powder and water-absorbing resin powder, in particular particles of the lubricating resin powder, are introduced between the components of the driving part to improve the compatibility between the components and thereby help the lubricating grease in lubricating the components. Consequently, in this case also, there is no need of replacing the components of the driving part of the driving mechanism in an early stage.
The high-lubricity grease proposed in the reference cited above, in which the solid lubricant consists mainly of polytetrafluoroethylene, has the following drawback. Since polytetrafluoroethylene is exceeding expensive as compared with the grease itself, the proposed high-lubricity grease is far more expensive than ordinary greases containing no solid lubricant (polytetrafluoroethylene).
Furthermore, not only high-lubricity greases but also ordinary greases have the property of absorbing water. Specifically, greases during use absorb water and hold it in an emulsified state. Because of this, in the high-lubricity greases containing polytetrafluoroethylene as a solid lubricant, the water held therein gradually reacts with the polytetrafluoroethylene with the aid of considerable frictional heat to generate hydrogen fluoride. The hydrogen fluoride generated acts on the high-hardness metallic parts being lubricated, e.g., a bearing made of stainless steel. The hydrogen fluoride destroys the passive-state surface film to accelerate corrosion of inner parts, and the resultant products of corrosion are released from the metallic parts and come into the grease. Consequently, the high-lubricity greases heretofore in use have the possibilities of corroding the parts being lubricated and of causing the parts to wear by the actin of the products of corrosion.
Accordingly, an aim of a second aspect of the invention is to eliminate those problems of high-lubricity greases heretofore in use. Namely, the aim is to provide a high-lubricity grease which does not corrode the parts being lubricated. Another aim of the second aspect of the invention is to enable a high-lubricity grease having such properties to be provided at a lower cost than this kind of high-lubricity greases heretofore in use.
The second aspect of the invention provides a high-lubricity grease which comprises a grease containing a solid lubricant therein, the solid lubricant comprising one or more synthetic resins selected from the group consisting of polyamides, polyimides, high-density polyolefins, and polyesters. Examples of the solid lubricant contained in the high-lubricity grease of the second aspect of the invention include synthetic resins such as aliphatic polyamides, e.g. nylons, aromatic polyamides, high-density polyethylene and polypropylene, and diallyl phthalate resins.
The high-lubricity grease of the second aspect of the invention contains one or more of those synthetic resins as the solid lubricant. The content of the synthetic resins is preferably from 1 to 50 parts by weight per 100 parts by eight of the grease.
The high-lubricity grease of the second aspect of the invention contains as a solid lubricant at least one synthetic resin selected from polyamides, polyimides, high-density polyolefins, polyesters, and the like. This solid lubricant, which comprises such synthetic resin(s), is inexpensive as compared with polytetrafluoroethylene, which is employed as a solid lubricant in the known high-lubricity greases. Furthermore, those synthetic resins for use as the solid lubricant in the second aspect of the invention have no or little reactivity with water even at high temperatures attributable to the frictional heat generating during use, and hence generate no harmful substance which may corrode the parts being lubricated. Therefore, the high-lubricity grease of the second aspect of the invention is a grease which neither corrodes the parts being lubricated nor causes the parts to wear by the action of products of corrosion. In addition, the high-lubricity grease can be provided at a low cost.
The modifier of the first aspect of the invention can be used for the grease of the second aspect of the invention can used.